Wave Velocity Field Research Articles

The layout of submerged horizontal plate breakwater (SHPB) with respect to the tidal-level variation

ABSTRACTThe submerged horizontal plate is widely regarded as an open-type breakwater and shows a sensitivity to tidal-level variation. However, nearly all existing studies assume a constant water level, which is deviated from the real situation. The present work conducts the pioneer investigation on the layout of the submerged horizontal plate breakwater (SHPB) with respect to tidal-level variation. It is carried out by using the smoothed particle hydrodynamics (SPH) method. A novel multilayer dynamic boundary particles (DBPs) technique is proposed for implementing the thin-wall boundary condition of the plate, accompanied by the approach of wave force calculation. A dam-break impact problem is first used to verify the multilayer DBPs technique. Then an experiment concerning solitary wave incidents on a submerged horizontal plate is numerically reproduced. Good agreements between the calculated and experimental wave profiles, hydrodynamic pressures, and wave forces are obtained. By applying the well-validated model, the effect of tidal-level variation on hydrodynamic characteristics of the SHBP, including the wave transmission coefficient, the pressure and velocity fields and the wave force, are investigated. On that base, the suggested layout of the SHBP with respect to the tidal range is given.

Assessment of the cyclic strain approach for evaluating liquefaction triggering

The cyclic strain approach was proposed in the 1980s as a potential alternative to the stress-based simplified liquefaction evaluation procedure. However, despite its fundamental basis and many positive attributes, it has not been embraced by practice. One reason for this may be the need to perform cyclic laboratory tests on undisturbed/reconstituted samples to develop a relationship among excess pore water pressure, cyclic strain amplitude, and number of applied strain cycles. Herein an alternative implementation of the strain-based procedure is proposed that circumvents this requirement, using a strain-based pore pressure generation model in lieu of laboratory test data. To assess the efficacy of the alternative implementation, several hundred small strain shear wave velocity (Vs) and Standard Penetration Test (SPT) field liquefaction case histories are evaluated. The results are compared with both field observations and with predictions from the stress-based procedures. It was found that the stress-based approach yielded considerably more accurate predictions compared to the cyclic strain approach. One likely reason for this is the strain-based procedure's inherent and potentially fatal limitation of ignoring the decrease in soil stiffness due to excess pore pressure when representing the earthquake loading in terms of shear strain amplitude and number of equivalent cycles.

New parameterizations for Bayesian seismic tomography

In this study, we rely on a Bayesian approach to estimate the seismic velocity from first arrival travel times. The advantage of the Bayesian approach compared to linearized ones is its ability to properly quantify the uncertainties associated with the solution. However, this approach remains fairly expensive, and the Markov chain-Monte Carlo algorithms that are used to sample the posterior distribution are efficient only when the number of parameters remains within reason. Therefore, a first step toward an efficient implementation of the Bayesian approach is to properly parameterize the model to reduce its dimensionality. In this article, we introduce new parsimonious parameterizations which enable us to accurately reproduce the wave velocity field and the associated uncertainties. The first parametric model that we propose uses a random Johnson–Mehl tessellation, a generalization of the Voronoi tessellation. The main difference of the Johnson–Mehl model when compared to the Voronoi model is that the shapes of the generated cells are much more general. The cells of a Voronoi tessellation are indeed convex polytopes, while the Johnson–Mehl tessellation model yields cells whose boundaries are portions of hyperboles and which are not necessarily convex, hence allowing for a greater variety of shapes. We demonstrate the gain in efficiency and the better convergence when compared to the Voronoi model. The second parameterization uses Gaussian kernels as basis functions. Its purpose is to provide a way to reproduce localized variations in the seismic velocity field. We first illustrate the tomography results with a synthetic velocity model which contains two small anomalies. We then apply our methodology to a more advanced and realistic synthetic model that serves as a benchmark in the oil industry. We finally present an example where Gaussian kernels outperform Voronoi and Johnson–Mehl models. The tomography results reveal the ability of our algorithm to map the velocity heterogeneities accurately using few parameters.

Steady solution of the velocity field of steep solitary waves

The steady solutions of solitary waves are studied through the use of the Irrotational Green–Naghdi (IGN) equations for an incompressible and inviscid fluid. The steady solutions are obtained by Newton–Raphson method. We consider the solitary gravity waves of H/h = 0.30, 0.50, 0.70, 0.79, 0.8296, 0.833199 (where H is the wave amplitude and h is the water depth). Some experiments are conducted to test the results of the IGN equations. In particular, we focus on the wave profile and velocity field. We find that for the cases of the solitary waves of H/h ≤ 0.79, the IGN-5 results agree very well with the Euler solutions. For the solitary waves that close to the maximum amplitude, the converged IGN results are presented. It is also shown that high level IGN results on wave speed agree well with the results obtained by others.

Assessment of soil compaction properties based on surface wave techniques

Soil compaction plays an important role in every construction activities to reduce risks of any damage. Traditionally, methods of assessing compaction include field tests and invasive penetration tests for compacted areas have great limitations, which caused time-consuming in evaluating large areas. Thus, this study proposed the possibility of using non-invasive surface wave method like Multi-channel Analysis of Surface Wave (MASW) as a useful tool for assessing soil compaction. The aim of this study was to determine the shear wave velocity profiles and field density of compacted soils under varying compaction efforts by using MASW method. Pre and post compaction of MASW survey were conducted at Pauh Campus, UniMAP after applying rolling compaction with variation of passes (2, 6 and 10). Each seismic data was recorded by GEODE seismograph. Sand replacement test was conducted for each survey line to obtain the field density data. All seismic data were processed using SeisImager/SW software. The results show the shear wave velocity profiles increase with the number of passes from 0 to 6 passes, but decrease after 10 passes. This method could attract the interest of geotechnical community, as it can be an alternative tool to the standard test for assessing of soil compaction in the field operation.

Imaging the total wavefields by reflectivity estimation using amplitude-normalized wavefield decomposition: Field data example

To combine imaging information of up- and downgoing wavefields using primaries and multiples, we have developed an imaging framework based on the subsurface impulse response. The latter is expressed at every depth level by a Fredholm integral equation defined in terms of the amplitude-normalized upgoing pressure and downgoing vertical velocity wavefields. The subsurface impulse response can be obtained by inverting the matrix form of the integral equation. By performing a multidimensional deconvolution (MDD) of the upgoing components by the downgoing components, this procedure gives the reflectivity matrix. By assuming locally reacting media or lateral shift invariance, we can describe how the MDD can reduce to simpler deconvolution imaging conditions. Based on an example acquired with dual-sensor towed streamers and simultaneous sources, we have developed a real data application of imaging the total up- and downgoing wavefields by reflectivity inversion. The total upgoing wavefield used in the imaging scheme is composed of the scattered energy from primaries and multiples. The primary reflected wavefield is generated by a direct downgoing source wavefield, which is mostly passing the acquisition surface at offsets smaller than the nearest data channel. Hence, the most relevant part of the direct wavefield is not measured in the studied example. From near-field pressure measurements, we predict the missing direct arrivals needed to image the primary reflected wavefield; we then synthesize the total downgoing wavefield by adding the downgoing scattered energy. By downward extrapolating the total up- and downgoing wavefields, a structural image is obtained by extracting the zero-spatial and temporal lags of the reflectivity matrix (computed by MDD of the decomposed wavefields). The obtained image is compared with the results computed from deconvolution imaging conditions. Furthermore, calculating the reflectivity matrix naturally allows for extracting the angle-dependent information of the subsurface.

Numerical simulation of heat transfer and determination of critical heat fluxes at nonsteady heat generation in falling wavy liquid films

In the current work, we present the mathematical model, which allows the calculation of the wave surface profile, velocity and temperature fields as well as the study of their evolution at a drastic change in heat loads with time. This model allows calculations of the wave characteristics and parameters of liquid film decay at different regime parameters.Using the presented model, we have simulated the wave formation process in falling film of liquid nitrogen and retrieved the resulting average wave characteristics for different inlet Reynolds numbers. We have also calculated the dependencies of boiling expectation time and total local evaporation time in falling wavy films of liquid nitrogen on heat flux density for different inlet Reynolds numbers.It was found out that all calculated dependencies are approximately similar in the area of high heat flux rates for all examined inlet Reynolds numbers indicating the weak influence of irrigation rate on boiling expectation time in this range of heat loads. Discrepancy of calculated dependencies was found in the area of low heat flux rates, what could be explained by significant influence of evaporation on heat transfer under such conditions. The dependencies of characteristic heat flux density of boiling suppression and total local evaporation suppression on the inlet Reynolds number were also presented.The regime map, which defines the different mechanisms of decay of falling wavy film of liquid nitrogen, was obtained by summing up the results of numerical simulation. The results of numerical simulations are in satisfactory agreement with experimental data.

Wave breaking in the surf zone and deep-water in a non-hydrostatic RANS model. Part 1: Organized wave motions

We examine wave-breaking predictions ranging from shallow- to deep-water conditions using a non-hydrostatic σ-coordinate RANS model NHWAVE as described in Derakhti et al. (2016a), comparing results both with corresponding experiments and with the results of a volume-of-fluid (VOF)/Navier-Stokes solver (Ma et al., 2011; Derakhti and Kirby, 2014a,b). Our study includes regular and irregular depth-limited breaking waves on planar and barred beaches as well as steepness-limited unsteady breaking focused wave packets in intermediate and deep water. In Part 1 of this paper, it is shown that the model resolves organized wave motions in terms of free-surface evolution, spectral evolution, organized wave velocity evolution and wave statistics, using a few vertical σ-levels. In addition, the relative contribution of modeled physical dissipation and numerical dissipation to the integral breaking-induced wave energy loss is discussed. In steepness-limited unsteady breaking focused wave packets, the turbulence model has not been triggered, and all the dissipation is imposed indirectly by the numerical scheme. Although the total wave-breaking-induced energy dissipation is underestimated in the unsteady wave packets, the model is capable of predicting the dispersive and nonlinear properties of different wave packet components before and after the break point, as well as the overall wave height decay and the evolution of organized wave velocity field and power spectrum density over the breaking region. In Part 2 (Derakhti et al., 2016b), model reproduction of wave-breaking-induced turbulence and mean circulation is examined in detail. The same equations and numerical methods are used for the various depth regimes, and no ad-hoc treatment, such as imposing hydrostatic conditions, is involved in triggering breaking. Vertical grid resolution in all simulated cases is at least an order of magnitude coarser than that of typical VOF-based simulations.

NHWAVE: Consistent boundary conditions and turbulence modeling

Large-scale σ-coordinate ocean circulation models neglect the horizontal variation of σ in the calculation of stress terms and boundary conditions. Following this practice, the effects of surface and bottom slopes in the dynamic surface and bottom boundary conditions have been usually neglected in the available non-hydrostatic wave-resolving models using a terrain-following grid. In this paper, we derive consistent surface and bottom boundary conditions for the normal and tangential stress fields as well as a Neumann-type boundary condition for scalar fluxes. Further, we examine the role of surface slopes in the predicted near-surface velocity and turbulence fields in surface gravity waves. By comparing the predicted velocity field in a deep-water standing wave in a closed basin, we show that the consistent boundary conditions do not generate unphysical vorticity at the free surface, in contrast to commonly used, simplified stress boundary conditions developed by ignoring all contributions except vertical shear in the transformation of stress terms. In addition, it is shown that the consistent boundary conditions significantly improve predicted wave shape, velocity and turbulence fields in regular surf zone breaking waves, compared with the simplified case. A more extensive model-data comparison of various breaking wave properties in different types of surface breaking waves is presented in companion papers (Derakhti et al., 2016a,b).

Characteristics Analysis of Load Caused by Punching Pile Construction of Highway Bridge Pile Foundation

The characteristics of impact loads caused by punching pile construction of highway bridge pile foundation and the propagation law of vibration wave in the soil were researched. Combined with site monitoring vibration signal which is generated by the bridge pile foundation construction of Zhang Shi Expressway across the Shaanxi Beijing pipeline, signal waveforms of the punching pile construction and blasting construction were analyzed contrastively. It expounded the characteristics of impact loads, and deduced the mathematical expressions of impact loads. On the basis of the analysis model, through the numerical simulation, the propagation law of vibration wave in the soil caused by the impacting point source excitation was revealed. Thus, it indicates that because of the buried pipeline, the local gradient of vibration wave velocity field increased in the area between the vibration source and the pipeline, but decreased in the far direction.

Method of shock wave overpressure reconstruction

A method of shock wave overpressure reconstruction is presented, which allows overcoming the drawbacks of the previous approaches associated with the lack of shock wave velocity measurement points and the limitations of the empirical formula. An optimal design of the testing system is proposed. Based on the optimal system, the shock wave velocity field is inverted with the use of the generalized inversion theory, and the overpressure distribution is obtained. The inversion results are preferable to empirical results because the experimental data are confirmed in a limited area. Methods of overpressure computation and visualization are described.

Ionospheric response to infrasonic‐acoustic waves generated by natural hazard events

AbstractRecent measurements of GPS‐derived total electron content (TEC) reveal acoustic wave periods of ∼1–4 min in the F region ionosphere following natural hazard events, such as earthquakes, severe weather, and volcanoes. Here we simulate the ionospheric responses to infrasonic‐acoustic waves, generated by vertical accelerations at the Earth's surface or within the lower atmosphere, using a compressible atmospheric dynamics model to perturb a multifluid ionospheric model. Response dependencies on wave source geometry and spectrum are investigated at middle, low, and equatorial latitudes. Results suggest constraints on wave amplitudes that are consistent with observations and that provide insight on the geographical variability of TEC signatures and their dependence on the geometry of wave velocity field perturbations relative to the ambient geomagnetic field. Asymmetries of responses poleward and equatorward from the wave sources indicate that electron perturbations are enhanced on the equatorward side while field aligned currents are driven principally on the poleward side, due to alignments of acoustic wave velocities parallel and perpendicular to field lines, respectively. Acoustic‐wave‐driven TEC perturbations are shown to have periods of ∼3–4 min, which are consistent with the fraction of the spectrum that remains following strong dissipation throughout the thermosphere. Furthermore, thermospheric acoustic waves couple with ion sound waves throughout the F region and topside ionosphere, driving plasma disturbances with similar periods and faster phase speeds. The associated magnetic perturbations of the simulated waves are calculated to be observable and may provide new observational insight in addition to that provided by GPS TEC measurements.

Study on Nonlinear Response of Steel Fixed Offshore Platform Under Environmental Loads

The structural design requirements of a fixed offshore platform subjected to wave-induced forces and moments in steel jacket can play a major role in the design of the offshore structures. For an economic and reliable design, good estimation of wave loadings is essential. Wave plus current kinematics are generated using fifth-order Stokes wave theory. The horizontal components of the wave velocity and acceleration fields are multiplied by a wave kinematics factor that is intended to account for direction spreading and irregularity of the wave profile. The wave and current forces acting on the member is computed using Morison’s equation, which decomposes the total force into an inertia component and a drag component. A nonlinear response analysis of a fixed offshore platform under wave loadings is presented; the structure is discretized using the finite element method. The dynamic response of fixed offshore structure together with the distribution of displacement, axial force, and bending moment along the leg is investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the 1-year return period wave and must be able to survive the 100-year return period storm conditions. The result of the study shows that the nonlinear response investigation is quite crucial for safe design and operation of offshore platform.

New Method for Imaging and Inversion of Interval Velocity

In order to obtain accuracy interval velocity and improve the quality of imaging of velocity volume, so as to better describe the geological structure and reservoir of gas hydrate in specific area, a new interval velocity inversion combination method is proposed in this paper. By introducing wave ray tracing algorithm and velocity field structuring and smoothing algorithm, this new inversion solution can deduce more accuracy and reasonable interval velocity than other normal inversion methods. Empirical results shows that velocity profile has higher resolution and can finely reflect the occurrence status and spatial distribution of gas hydrate.

Numerical analysis of the relationship between time-variant coda-Q and the variation in crustal stress

SUMMARY Coda-Q is a stochastic parameter reflecting the heterogeneities of medium that seismic waves travel through. We confirmed that coda-Q would vary with the stress loaded to an elastic medium using numerical simulations of seismic wave propagation. When the stress is loaded, cracks in the crust could either close or newly open. The closure and opening of the cracks are not random but depending on the magnitude and the direction of the stress and the crack aspect ratio. The cracks in the medium after loading stress could be aligned in a specific orientation, and elastic wave velocity field would become anisotropic due to the alignment of specific crack orientations. Elastic wave velocity is in general faster along the direction corresponding with the crack orientation while slower along the perpendicular direction. In the numerical simulation, the effect of anisotropy in elastic wave velocity field due to the selective closure and opening of the cracks is calculated using a 2-D finite difference method assuming elastic wave velocity to be a function of the magnitude of loaded stress. The coda-Q calculated from seismic waves simulated for a model varies when the averaged normal stress changes. Our simulation indicated that the sensitivity of coda-Q −1 , that is the reciprocal of the coda-Q, would be 1.0 × 10 −2 (1.0MPa ‐1 ) against the magnitude of the confining pressure and 1.0 × 10 −3 (1.0 deg ‐1 ) against the direction of principal stress. We would like to conclude that coda-Q, a stochastic parameter reflecting heterogeneities of subsurface medium, could become a quantitative state indicator of the stress field of the medium where seismic waves propagate through. Spatiotemporal variation of coda-Q reflects change in the stress field in the crust.

Numerical modeling of groin impact on nearshore hydrodynamics

Groins are cross shore structures built to promote shoreline stabilization. However, the specific impact of these structures on the wave conditions and velocity field nearshore (and hence, on sediment transport) is still poorly understood. Therefore, this study wishes to extend this knowledge using a numerical model, COULWAVE, previously validated with field data. For that, a typical bar-trough profile is considered and different groin lengths and orientations are tested, under the influence of different significant incident-wave heights and sea-surface levels.The hydrodynamics factors are found to have a greater impact on the nearshore wave conditions than the groin geometry. The variation of significant incident-wave height imparts the greater changes in wave height nearshore, where the groin would be located. The typical tidal range is also important, since a 2m change in sea surface level can cause great depth changes over bathymetric features and thus influence wave propagation. Although less important, the geometry of the groin should also be considered. The greater the length, the greater the sheltering effect expected, extending further to the lee-side of the groin. The impact will also reach a broader region. With a smaller impact verified, the best orientation of the groin is hard to unravel.

3D Stereoscopic PIV visualization of the axisymmetric conical internal wave field generated by an oscillating sphere

To date, experimental studies of internal wave velocity fields have been limited to two-dimensional investigations of planar or axisymmetric systems. Here, we present results of the first three-dimensional stereoscopic Particle Image Velocimetry (PIV) visualizations of an internal wave field. The experiments utilize the canonical arrangement of a vertically oscillating sphere, which enables rigorous comparison with recently published theoretical results. The excellent level of agreement between experiment and theory demonstrates the utility of using stereoscopic PIV to study three-dimensional internal waves. Furthermore, the ability to measure all three components of the velocity field gives an alternative perspective on the significance of harmonics generated via nonlinear processes in the vicinity of the oscillating sphere.

Determination of Shear Wave Velocity and Depth to Basement Using Multichannel Analysis of Surface Wave Technique

Abstract The dispersive characteristics of Rayleigh type surface waves were utilized to estimate shear wave velocity (Vs) profile followed by imaging the shallow subsurface granitic layers in the heart of Hyderabad. The reliability of Multichannel Analysis of Surface Waves (MASW) depends on the accurate determination of phase velocities for horizontally traveling fundamental mode Rayleigh waves. Multichannel recording leads to effective identification and isolation of various factors of noise. Calculating the 1-D shear wave velocity (Vs) field from surface waves ensures high degree of accuracy irrespective of cultural noise. The main advantage of mapping the bed rock surface with shear wave velocity (Vs) is the insensitivity of MASW to velocity inversion besides being free from many constraints such as contrast in physical properties etc. Modeling of surface waves data results a shear wave velocity (Vs) of 250-750 m/s covering the top soil to weathering and up to bedrock corresponding to a depth range of 10-30 m. Further, the computed N values (which is an indicator of site characteristic) based on the harmonic shear wave velocity up to a depth of 5 m is found to be quite high (> 25-30) well above 5 indicating the site to be safe and strong enough and not prone to liquefaction. A pair of selected set of results over granites are presented here as a case study highlighting the salient features of MASW.

Direct measurement of ocean waves velocity field from a single SPOT-5 dataset

We present a method based on space-borne optical imagery from the SPOT5 satellite to directly measure the phase velocity fields of ocean waves. The panchromatic and multispectral scenes acquired by SPOT5 the same day on the same area are not strictly superimposable due to the different locations of the CCDs (Charged Coupled Device) in the focal plane of the instrument. In this manuscript, we propose a method that exploits the temporal lag that exists between the panchromatic and multispectral scenes to measure the ocean wave velocity fields. We firstly discuss the principle and the methodology. Then, we apply it offshore La Reunion Island. Finally, we compare and discuss the results against a swell propagation model. Our method is proven reliable and can be immediately extended to other push-broom sensors.

Analysis of the interference effects for high-speed catamarans by model tests and numerical simulations

This paper presents the results of a large experimental and numerical campaign aimed to the analysis of the interference effect for a fast catamaran. Several separation distances are considered; data for resistance, sinkage and trim are collected by towing tank experiments for Froude number ranging from 0.2 to 0.8. Monohull tests are also carried out, the analysis of the interference and its dependency on the separation length being the main objective of the paper. Resistance coefficient curves reveal the presence of two humps, the second one strongly depending on the separation length; high interference is observed in correspondence of the second hump. It is found that the narrower is the configuration, the higher is the interference and the speed at which this maximum occurs. To gain a deeper insight into these behaviors, a complementary analysis, in terms of wave field, surface pressure and velocity field is carried out by an in-house unsteady RANS solver. Verification of numerical results is provided, together with validation, which is made by the comparison with both present and other experimental data. Agreement in terms of resistance coefficient is rather good, comparison error being always smaller than 2.2%.